CN104808192A - Swing device for three-dimensional laser scanning and its coordinate conversion method - Google Patents

Abstract

The invention discloses a swinging device for three-dimensional laser scanning and a coordinate conversion method thereof.A two-dimensional laser scanner is fixed on a radar swinging support, the radar swinging support is connected with a swinging control device shell through a rotating bearing, the rotating bearing is fixedly connected with the side wall of the swinging control device shell, a steering engine for supporting an encoding disk and an embedded control panel are arranged in the swinging control device shell, the steering engine for supporting the encoding disk is connected with the embedded control panel, and an inertia measurement unit for tracking the pose change of the whole system is fixed on the swinging control device shell. By accurately calculating the swing angle of the swing device, three-dimensional data of the whole space is obtained while the laser swings. The two-dimensional scanning realized by the swinging device has higher cost performance than that of a three-dimensional laser scanner, the volume is relatively light, the position of the scanner can be obtained through data registration while three-dimensional data is obtained, and the synchronous acquisition and positioning technology of a map is solved.

Description

Swing device for three-dimensional laser scanning and its coordinate conversion method

technical field

The invention belongs to the technical field of surveying and mapping, and relates to a swing device for three-dimensional laser scanning by using a two-dimensional laser scanner, and also relates to a coordinate conversion method of the swing device for three-dimensional laser scanning.

Background technique

The laser radar emits pulsed laser light in all directions in the plane by rotating the mirror and receives the reflected light by the laser receiver. The time difference between reflection and reception is calculated by a timer to measure the distance from the obstacle to the radar.

HOKUYO's 30LX lidar can realize two-dimensional 270° plane scanning and detect obstacles up to 30m away. This type of radar is used in smart vehicles to detect obstacles or other vehicles in front of the vehicle, so that smart vehicles can avoid obstacles or other vehicles and maintain a safe driving distance. HOKUYO-30LX radar emits a laser beam at a certain frequency within 270° of the plane, and when it encounters an obstacle, it reflects the beam and is received by the laser receiver, so as to obtain the information of one or more points of the obstacle in the scanning plane. Using this information, the distance (depth) and width information of the obstacle can be obtained, but the height information is not known; in addition, if the obstacle is not in the scanning plane, the obstacle cannot be detected, and only the distance of the obstacle on the scanning plane can be obtained (depth) and width information, but cannot get any information in the height direction, and cannot accurately identify obstacles and perceive the three-dimensional environment.

Three-dimensional laser scanners can obtain data information in the entire three-dimensional space. However, three-dimensional laser scanners are generally expensive and relatively large in size. When performing 3D laser scanning, it is often a "stop and go" type of scanning and must be scanned at a pre-set location. However, in some special environments, such as mines or caves, more convenient and smart hand-held laser mapping equipment is often required. Therefore, the industry urgently needs to develop a method that can change the limitations of HOKUYO radar in such applications, and transform the two-dimensional lidar into a lidar capable of mobile three-dimensional scanning.

Contents of the invention

The object of the present invention is to provide a swing device that utilizes a two-dimensional laser scanner for three-dimensional laser scanning, and converts two-dimensional laser radar into a three-dimensional scanning laser radar; the distance (depth) and width of obstacles on the scanning plane can be obtained At the same time, the information in the height direction is obtained, which is convenient for the radar to identify obstacles and perceive the three-dimensional environment.

Another object of the present invention is to provide a coordinate conversion method of a swing device for three-dimensional laser scanning.

In order to achieve the above object, the present invention is achieved through the following technical solutions: a swing device for three-dimensional laser scanning using a two-dimensional laser scanner, the two-dimensional laser scanner is fixed on the radar swing bracket, and the radar swing bracket and the swing control device shell pass through The rotating bearing is connected, and the rotating bearing is fixedly connected to the side wall of the swing control device shell. Inside the swing control device shell, a steering gear supporting the code disc and an embedded control board are arranged. The steering gear supporting the code disc is connected with the embedded control board to track the entire The inertial measurement unit of the system's pose change is fixed on the shell of the swing control device.

The invention is also characterized in that the axis of the rotating bearing is located on the physical center plane of the emission of the radar laser beam of the two-dimensional laser scanner.

The external connection of the swing control device shell is a 12V power supply and serial port communication, and the serial port is connected with the computer.

The 2D laser scanner is HOKUYO-30LX radar.

Another technical solution adopted in the present invention is that the coordinate conversion method of the swing device for three-dimensional laser scanning is carried out according to the following steps:

step 1,

After reading the laser data each time, record the acquisition time of the laser data and set it as t ₁ ; at the same time, read the serial port data immediately to obtain the current swing position of the swing device, and set the time after reading the data as t ₂ ;

Step 2,

Assuming that the angles of the oscillating device corresponding to the two adjacent acquisitions of laser data are a ₁ , a ₂ ; the corresponding times are t ₁ , t ₂ respectively, then the approximate angular velocity of the oscillating device is w=(a ₁ -a ₂ )/ (t ₁ -t ₂ );

Step 3,

Between the acquisition of the laser data and the corresponding swing angle data, assuming that the angle of the corresponding value is A and the time is T, the swing device actually continues to swing more diffA=A-(T-0.01)*w, the real swing of the swing device The angle is B=A-diffA, so far the error compensation of the swing device is completed;

Step 4,

Due to the swing of the oscillating device, for the points within one swing cycle of the laser, the swing track is the curve θ*sinθ, assuming that the ideal scanning point before the laser finishes the last scan is the line segment AB, and the ideal scanning point after one cycle is the line segment CD , and the actual point is the dotted line between AB and CD. For the real scanning point E, its deflection angle θ relative to the CD coordinate axis can be obtained from its coordinates (x, y); and its deflection angle θ relative to the AB coordinate axis The shift angle is γ=α-θ;

Step 5,

For the point E whose deflection is γ relative to the AB coordinate axis, multiply the rotation matrix to obtain the coordinates (x ₁ , y ₁ ) of the point E under the coordinate axis AB,

x ₁ =cos(θ)*x–sin(θ)*y

y ₁ =sin(θ)*x+cos(θ)*y

$\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\\ \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; *</span>\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; x</span>}\\ \mathrm{<span\; class="notranslate">\; the\; y</span>}\\ \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]$

Apply the transformation method in step 5 to all scanning points, and then transfer the coordinates of the laser scanning points from the laser coordinate system to the world coordinate system.

The beneficial effect of the present invention is that by accurately calculating the swing angle of the swing device, three-dimensional data of the entire space can be obtained while the laser is swinging. The two-dimensional scanning realized by using the swing device is not only more cost-effective than the three-dimensional laser scanner, but also its volume is relatively light. While obtaining the three-dimensional data, the position of the scanner can be obtained through data registration, which solves the problem of synchronous map acquisition and Positioning Technology.

Description of drawings

Figure 1 is a schematic diagram of laser data coordinate transformation.

Fig. 2 is a structural schematic diagram of the present invention.

In the figure, 1. Two-dimensional laser scanner, 2. Inertial measurement unit, 3. Embedded control board, 4. Radar swing bracket, 5. Steering gear supporting code disc, 6. Rotary bearing, 7. Swing control device housing .

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

A swing device using a two-dimensional laser scanner for three-dimensional laser scanning, the structure of which is shown in Figure 2, consists of a two-dimensional laser scanner 1, an inertial measurement unit 2 (IMU), an embedded control board 3, a radar swing bracket 4, The steering gear 5 that supports the code disc, the rotating bearing 6, and the swing control device housing 7 that encapsulates the embedded control board 3 and the steering gear 5 that supports the code disc are composed.

Two-dimensional laser scanner 1 is HOKUYO-30LX radar.

The radar swing bracket 4 is connected to the swing control device housing 7 through a rotating bearing 6, and the rotating bearing 6 is fixedly connected to the side wall of the swing control device housing 7. The inside of the swing control device housing 7 is provided with a steering gear 5 and an embedded control board 3 supporting the code disc. The radar swing bracket 4 is fixed on the rotating bearing 6 of the steering gear. The swing direction and angle of the steering gear 5 supporting the code disc are determined by the embedded Type control board 3 to control. An inertial measurement unit 2 is fixed on the front of the swing control mechanism in the vertical direction, and the inertial measurement unit 2 is fixed on the shell 7 of the swing control device to track the pose changes of the entire system.

In the vertical swing control mechanism, the embedded control board 3 is connected to the steering gear 5 supporting the code disc, and the axis of the rotating bearing 6 is located on the physical center plane where the radar laser beam of the two-dimensional laser scanner 1 is emitted.

The swing angle of the radar swing bracket 4 is plus or minus 90°, that is, it swings back and forth between plus or minus 90°, the swing is variable speed swing, and the whole swing period is controlled within 1 second. The swing angle is tracked in real time by the encoder disc, accurate to 0.025 degrees.

Wherein the two-dimensional laser scanner 1 is fixed on the radar swing bracket 4, and the radar swing bracket 4 and the rotating bearing 6 are tightly fixed. Note here that the axis of the rotating bearing 6 is located on the physical center plane of the radar laser beam emitted by the two-dimensional laser scanner 1, which ensures that the mechanical swing angle is consistent with the laser beam swing angle up and down, and reduces the complexity of three-dimensional imaging calculations. The rotating bearing 6 is controlled by the steering gear 5 supporting the code disk, and the specific rotation frequency of the steering gear 5 supporting the code disk is determined by the commands written by the embedded control board 3 through the serial port. The steering gear 5 and the embedded control board 3 supporting the code disc are packaged in the swing control device shell 7 . The external connection of the swing control device shell 7 includes a 12V power supply and serial port communication, wherein the serial port adopts the RS232 protocol with a baud rate of 115200, and the serial port is connected with a computer for reading swing angle data and issuing control commands. On the housing 7 of the swing control device, an inertial measurement unit 2 is fixed for recording the pose of the swing device. The swing angle of the radar swing bracket 4 is plus or minus 90°, the swing period is 1 second, and the swing surface swings at a variable speed within 180°. The swing angle at a certain moment can be accurately obtained by using the angle sensor and angle derivation algorithm.

Working principle: For the radar, all it obtains are coordinates relative to its own center position as the origin. In order to achieve data registration, it is necessary to convert these points to the current actual swing angle. So the exact swing angle needs to be known. However, due to the inconsistency between the frequency of the swing device and the radar data, that is, when we obtain the radar data, due to the frequency difference between the radar and the swing device, the sampling frequency of the swing is 100HZ, and the frequency of the laser is 40HZ. After obtaining a laser data, immediately query the swing. Angle, up to a difference of 0.02 seconds. Because in order to ensure that there is a complete angle record in the read data, one more data is required in actual operation. 0.02 seconds includes 0.01 seconds waiting for the arrival of data and 0.01 seconds waiting for the second piece of data to be read. But this 0.02 seconds may also cause a huge deviation in point cloud registration. Assuming that the laser swings 360 degrees per second, there is an error of 7.2 degrees in 0.02 seconds. In addition, when the prism inside the laser rotates and scans, its scanning cycle (270 degrees) takes 0.025 seconds. In this time segment, because the laser is in a swing state, the difference between the first scanned point and the last scanned point is 9 degrees. .

In order to solve the precise synchronization between the laser and the oscillating device, the coordinate conversion method of the oscillating device for three-dimensional laser scanning is carried out according to the following steps:

step 1,

After reading the laser data each time, record the acquisition time of the laser data and set it as t ₁ ; at the same time, read the serial port data immediately to obtain the current swing position of the swing device. The time after reading the data is set to t ₂ ;

Step 2,

Assuming that the angles of the oscillating device corresponding to the two adjacent acquisitions of laser data are a ₁ , a ₂ ; the corresponding times are t ₁ , t ₂ respectively, then the approximate angular velocity of the oscillating device is w=(a ₁ -a ₂ )/ (t ₁ -t ₂ );

Step 3,

Between the acquisition of laser data and the corresponding swing angle data (assuming that the angle of the corresponding value is A and the time is T), the swing device actually continues to swing more diffA=A-(T-0.01)*w, here subtract 0.01 It is to compensate for the 0.01 second wait for obtaining the second piece of data, so the real swing angle of the swing device should be B=A-diffA, so far the error compensation of the swing device is completed.

Step 4,

Due to the swing of the swing device, for a point within one swing cycle of the laser, its swing trajectory is shown in the curve θ*sinθ, and the trajectory of the generated point is shown as the dotted line in Figure 1. Assume that the ideal scanning point before the last scan of the laser is the line segment AB, the ideal scanning point after one cycle is the line segment CD, and the actual point is the dotted line between AB and CD. For the real scanning point E, its deflection angle θ relative to the CD coordinate axis can be obtained from its coordinates (x, y); and its deflection angle relative to the AB coordinate axis is γ=α-θ;

Step 5,

For a point E with a deflection of γ relative to the AB coordinate axis, multiply the rotation matrix to obtain the coordinates (x ₁ , y ₁ ) of point E under the coordinate axis AB

x ₁ =cos(θ)*x–sin(θ)*y

y ₁ =sin(θ)*x+cos(θ)*y

$\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\\ \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; *</span>\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; x</span>}\\ \mathrm{<span\; class="notranslate">\; the\; y</span>}\\ \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]$

Apply the transformation method in step 5 to all scanning points, and then transfer the coordinates of the laser scanning points from the laser coordinate system to the world coordinate system. On this basis, related research such as 3D scene construction can be carried out.

Claims (5)

1. the pendulous device utilizing two dimensional laser scanning instrument to carry out 3 D laser scanning, it is characterized in that, two dimensional laser scanning instrument (1) is fixed on (4) on radar swinging mounting, radar swinging mounting (4) is connected by rolling bearing (6) with oscillating control device shell (7), rolling bearing (6) is affixed with oscillating control device shell (7) sidewall, oscillating control device shell (7) inside is provided with the steering wheel (5) and embedded control panel (3) of supporting code-wheel, support that the steering wheel (5) of code-wheel is connected with embedded control panel (3), the Inertial Measurement Unit (2) following the tracks of the pose change of whole system is fixed on oscillating control device shell (7).

2. a kind of pendulous device utilizing two dimensional laser scanning instrument to carry out 3 D laser scanning according to claim 1, it is characterized in that, the axis of described rolling bearing (6) is positioned in physical centre's plane of LIDAR bundle transmitting of two dimensional laser scanning instrument (1).

3. a kind of pendulous device utilizing two dimensional laser scanning instrument to carry out 3 D laser scanning according to claim 1, it is characterized in that, the power supply of the aerial lug 12V of described oscillating control device shell (7) and serial communication, serial ports is connected with computing machine.

4. a kind of pendulous device utilizing two dimensional laser scanning instrument to carry out 3 D laser scanning according to claim 1, is characterized in that, described two dimensional laser scanning instrument (1) is HOKUYO-30LX radar.

5., as a coordinate transformation method for the pendulous device of claim 1-5 as described in any one, it is characterized in that, carry out according to following steps:

Step 1,

After reading laser data at every turn, record the acquisition time of laser data, be set to t ₁; Read serial data at once, obtain the current oscillation position of pendulous device, the time of having read data is set to t simultaneously ₂;

Step 2,

If corresponding pendulous device angle is respectively a during adjacent twice acquisition laser data ₁, a ₂; The corresponding time is respectively t ₁, t ₂, then the approximate angular velocity of pendulous device is w=(a ₁-a ₂)/(t ₁-t ₂);

Step 3,

Obtaining between laser data pendulum angle data corresponding with it, suppose that the angle of respective value is A, time is T, pendulous device actual continuation plurality of pendulums has moved diffA=A-(T-0.01) * w, the real pendulum angle of pendulous device is B=A-diffA, so far complete to the error compensation of pendulous device;

Step 4,

Due to the swing of pendulous device, make for the point in the hunting period of laser, its swinging track is curve θ * sin θ, suppose laser terminate upper one scanning before ideal scan point be line segment AB, ideal scan point after one-period is line segment CD, and actual point is the dotted line between AB and CD, for real scan point E, its deflection angle θ relative to CD coordinate axis can be obtained by its coordinate (x, y); And it is γ=α-θ relative to the deviation angle of AB coordinate axis;

Step 5,

For the some E being deflected to γ relative to AB coordinate axis, take advantage of rotation matrix, obtain the coordinate (x of some E under coordinate axis AB ₁, y ₁),

x ₁＝cos(θ)*x–sin(θ)*y

y ₁＝sin(θ)*x+cos(θ)*y

$\left[\begin{array}{c}{x}_1\\ y_1\\ 1\end{array}\right]=\left[\begin{array}{ccc}\cos \left(\mathrm{\&theta;}\right)& -\sin \left(\mathrm{\&theta;}\right)& 0\\ \sin \left(\mathrm{\&theta;}\right)& \cos \left(\mathrm{\&theta;}\right)& 0\\ 0& 0& 1\end{array}\right]*\left[\begin{array}{c}x\\ y\\ 1\end{array}\right]$

To the conversion method in all analyzing spot applying steps 5, just the coordinate of laser scanning point is transferred to world coordinate system by laser coordinate system.